Static trip circuit breaker test set

Abstract

A field test set for static trip circuit breakers is electrically connected to the static trip unit and to the circuit breaker trip coil and phase current sensor transformers. The test set, powered from a low voltage source, is equipped to shunt feed the trip unit power supply, bringing the trip unit up to power preparatory to the injection of selected levels of overcurrent and ground fault simulating test signal current for verifying the time-current characteristics and current pickup calibrations of the various trip functions of the trip unit. A lockout circuit automatically terminates a test signal current whose magnitude and duration represents potential harm to the trip unit. The test set is also equipped to test the trip coil energization level developed by the trip unit and also the continuity of the breaker current transformers.

Having described my invention, what I claim as new and desire to secure by Letters Patent is: 
     
       1. A field test set for circuit breakers having phase current monitoring current transformers normally individually connected to supply phase current signals to separate phase signal inputs of a static trip unit for processing to determine the existence of an overcurrent condition, the trip unit including a power supply connected to the phase signal inputs for deriving trip unit operating power from the phase current signals and further including an output connected to supply tripping current for energizing a trip solenoid pursuant to initiating a trip function, said test set including, in combination: A. a variable source of test signal current;   B. a current meter;   C. a calibration circuit connected to receive said test signal current and having a voltage divider network developing a test signal voltage proportional to said test signal current for application to said current meter;   D. test selector switch means operating to selectively route said test signal current from said calibrating circuit to one of the trip unit phase signal inputs;   E. a power source supplying test power current to directly power up the trip unit power supply independently of the phase signal inputs; and   F. test logic circuitry operating to signal a successful execution of a test trip function in response to the receipt of an effective magnitude of tripping current generated at the trip unit output, said test logic circuitry further operating to coordinate the application of said test signal current and said test power current to the trip unit.   
     
     
       2. The test set defined in claim 1, which further includes an elapsed time meter operating under the control of said test logic circuitry for indicating the time interval from the initial application of said test signal current to the trip unit to the successful execution of a test trip function. 
     
     
       3. The test set defined in claim 1, which further includes overcurrent lockout circuitry for monitoring the application of test signal current to the trip unit, said lockout circuitry operating when the level and duration of said test signal current exceed predetermined limits to automatically impose a lockout restraint on said test logic circuitry, whereby said test logic circuitry terminates the application of said test signal current to the trip unit. 
     
     
       4. The test set defined in claim 3, wherein said overcurrent lockout circuitry includes a timing circuit for sustaining said lockout restraint on said test logic circuitry for a predetemined time duration following the termination of said test signal current. 
     
     
       5. The test set defined in claim 1, which further includes a phase current monitoring current transformer continuity check circuit selectively connectable to each of the circuit breaker current transformers and operating to check the electrical continuity thereof. 
     
     
       6. The test set defined in claim 1, wherein the trip unit further includes a differential current transformer having separate primary windings connected to be energized by the phase current signals and a secondary winding connected to supply a ground fault signal current to the trip unit in the event of an imbalance in the phase current signals, said test selector switch means being operable to route said test signal current to a primary winding of the trip unit differential current transformer to create a current imbalance and thereby verify the response of the trip unit to a ground fault signal current input. 
     
     
       7. The test set defined in claim 6, wherein the circuit breaker includes a neutral current monitoring current transformer normally connected to supply a neutral current signal to a neutral primary winding of the differential current transformer, said test selector switch means operable to route said test signal current through the neutral primary winding in verifying the trip unit response to a ground fault signal input. 
     
     
       8. The test set defined in claim 1, wherein said test logic circuitry includes timing circuit means operating to delay the application of said test signal current to said trip unit for a predetermined time following the application of said test power current to said trip unit, whereby the trip unit is powered up and capable of immediate response to the initial application thereto of said test signal current. 
     
     
       9. The test set defined in claim 1, wherein said test logic circuitry includes: (1) a start switch,   (2) a first relay having contacts controlling the application of test power current to the trip unit,   (3) a second relay having contacts controlling the application of test signal current to the trip unit,   (4) first means responsive to the closure of said start switch for initiating activation of said first relay, thereby conditioning its contacts to initiate the application of test power current to the trip unit, and   (5) second means responsive to the activation of said first relay for initiating activation of said second relay after a predetermined delay, whereupon said contacts of said second relay are conditioned to initiate the application of test signal current to the trip unit.   
     
     
       10. The test set defined in claim 9, wherein said test logic circuitry further includes: (1) a preset current switch operable to, in turn, render said second means operable to initiate application of said test signal current to the trip unit without prior activation of said first relay, thereby permitting adjustment of said variable source to establish a desired level of test signal current while the trip unit is unpowered.   
     
     
       11. The test set defined in claim 9, wherein said test logic circuitry further includes a level detecting circuit responsive to trip unit tripping current exceeding a predetermined level for deactivating said first and second relays pursuant to terminating the application of said test signal and test power currents to the trip unit. 
     
     
       12. The test set defined in claim 11, wherein said test logic circuitry further includes a selector switch operable in a first position to route the trip unit tripping current solely to said level detecting circuit and in a second position to route the trip unit tripping current to said level detecting circuit via the circuit breaker trip solenoid. 
     
     
       13. The test set defined in claim 11, which further includes an elapsed time meter, said second relay having additional contacts enabling the energization of said elaspsed time meter while said second relay is activated. 
     
     
       14. The test set defined in claim 11, which further includes overcurrent lockout circuitry monitoring the application of test signal current to the trip unit, said lockout circuitry operating, when the level and duration of said test signal current exceeds predetermined limits, to disable said first and second means and thereby deactivate said first and second relays, and said lockout circuitry including a timing circuit for sustaining the disablement of said first and second means for a predetermined limited duration. 
     
     
       15. The test set defined in claim 11, which further includes a phase current monitoring current transformer continuity check circuit selectively connectable to each of the circuit breaker current transformers and operating to check the electrical continuity thereof. 
     
     
       16. The test set defined in claim 11, wherein said test signal voltage developed in said calibrating circuit is effective in calibrating said current meter to read in multiples of the established continuous current rating of the trip unit. 
     
     
       17. The test set defined in claim 16, wherein said voltage divider network is adjustable to accommodate various, selectively established trip unit continuous current ratings.